Such convertible aircraft carry in the floor that separates the upper deck from the lower deck or freight space, support rails and the respective locking devices are releasably secured to the support rails. The conventional locking devices include at least one locking hook mounted in a frame which can be secured through locking mechanisms to two support rails extending in parallel to each other in the longitudinal aircraft or X-direction.
German Patent Publication (DE-PS) 3,107,745 corresponding to U.S. Pat. No. 4,457,649 (Vogg et al.), issued on Jul. 3, 1984, discloses a locking device of the type described above. The known locking device serves for the purpose of a so-called YZ-lock. Such a lock provides an arresting force in the Y-direction and in the Z-direction of a three-dimensional coordinate system the X-axis of which extends in the longitudinal aircraft direction. Thus, the so-called YZ-lock arrests a piece of freight, such as a pallet or container in its final loaded position in the cargo hold in the vertical direction, which is the Z-direction, and in the horizontal or lateral direction, which is the Y-direction. This arresting is accomplished by means of the locking hook which is constructed to reach over projections or into pockets of the respective container or pallet.
Freight containers and pallets used for this purpose are frequently standardized and the zones to be engaged by the locking hook, such as recesses or locking pockets, are so constructed and positioned that the locking hook which reaches into a locking pocket provides an arresting also in the X-direction, namely in the longitudinal aircraft direction in addition to the locking in the Y- and Z-directions. Locking arrangements capable of arresting a piece of freight in all three directions of space (X,Y,Z) are subject to the problem that the zones or areas on the pieces of freight which are to be engaged by the locking hook, may have a raster or grid division that may differ from a respective raster division in the support rails to which the locking devices are secured at uniform spacings from one another.